1. Field of the Invention
The present invention relates to an air conditioning system for an automobile for controlling the temperature of a cabin of an automobile operated selectively by an electric motor or by an internal combustion engine.
2. Description of Related Art
Known in the prior art is a so-called hybrid car that includes, for driving the car, both an electric motor and an internal combustion engine, wherein the electric motor is operated when in an urban area, and the internal combustion engine is operated when the car is in a suburb an area when the battery is low. In such a hybrid car, a heating operation for the cabin of the vehicle depends on the power source as selected. Namely, when the electric motor operates the automobile, the compressor is powered and driven by the electric battery. A condenser, which is arranged in an air duct so as to form a refrigerating cycle together with the compressor, operates as a heating device such that a heat exchange takes place between the condenser and the air passing through the duct so as to heat the air in the duct, which is discharged into the cabin for heating thereof. Otherwise, an electric heater is operated so that the air flowing in the duct is heated, which is discharged into the cabin for heating thereof. When the vehicle is operated by the internal combustion engine, a heater core, which is arranged in the duct, is supplied by hot, engine cooling water taken from an engine cooling water line that is subjected to a heat exchange with the air passing through the duct for heating thereof.
When the vehicle is driven by an electric motor, with the internal combustion engine not operating, the compressor is supplied by the battery assembly in such a manner that a so-called heat pump operation of a refrigerating cycle is obtained for heating the cabin. In this case, a low atmospheric air temperature results in the reduction of the efficiency of the heat pump causing electric power consumption to increase, which results in a reduction in travelling distance. The use of the electric heater in place of the above mentioned heat pump operation may usually further increase electric power consumption because the heating efficiency as obtained by the electric heater is lower than that obtained by the heat pump operation.